But I arrive at the Pathless Plain and stick my hand in the black void at exactly 00:00 on Thursday/ Friday. Do I get Cobalion or Virizion ?

The other question is that, if I had already caught Cobalion and I saved infront of the dark void on Thursday and left my Game. I come back to it in a bit on a Friday (around 00:05 or so)
would the void be there and I can catch Virizion or will I not be able to catch her ?